The vast majority of patients treated with conventional (C) cardiopulmonary resuscitation (CPR) never wake up after cardiac arrest. Traditional closed-chest CPR involves repetitively compressing the chest in the med-sternal region with a patient supine in an effort to propel blood out of the non-beating heart to the brain and other vital organs. This method is not very efficient, in part because refilling of the heart is dependent upon the generation of an intrathoracic vacuum during the decompression phase that draws blood back to the heart. C-CPR typically provides only 15-30% of normal blood flow to the brain and heart. In addition, with each chest compression, the arterial pressure increases immediately. Similarly, with each chest compression, right-side heart pressures rise to levels nearly identical to those observed on the arterial side. The high right-sided pressures are in turn transmitted to the brain via the paravertebral venous plexus and jugular veins. This increase in blood volume and pressure with each chest compression in the setting of impaired cerebral perfusion further increases intracranial pressure (ICP), thereby reducing cerebral perfusion. In addition, the simultaneous rise of arterial and venous pressure with each C-CPR compression generates contemporaneous bi-directional (venous and arterial) high pressure compression waves that bombard the brain within the closed-space of the skull. This has the potential to further reduce brain perfusion and cause additional damage to the already ischemic brain tissue during C-CPR.
To address these limitations, newer methods of CPR have been developed that significantly augment cerebral and cardiac perfusion, lower intracranial pressure during the decompression phase of CPR, and improve short and long-term outcomes. These methods may include the use of active compression decompression (ACD)+CPR, an impedance threshold device (ITD), and/or combinations thereof. However, despite these advances, most patients still do not wake up after out-of-hospital cardiac arrest.